linux-kernel - Re: BUG: mm, numa: test segfaults, only when NUMA balancing is on

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Date:	Sat, 23 Nov 2013 00:09:24 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	Alex Thorlton <athorlton@....com>
Cc:	Rik van Riel <riel@...hat.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: BUG: mm, numa: test segfaults, only when NUMA balancing is on

On Fri, Nov 22, 2013 at 11:05:24PM +0000, Mel Gorman wrote:
> On Fri, Nov 22, 2013 at 03:28:07PM -0600, Alex Thorlton wrote:
> > > If the warning added by that patch does *not* trigger than can you also
> > > test this patch? It removes the barriers which should not be necessary
> > > and takes a reference tot he page before waiting on the lock. The
> > > previous version did not take the reference because otherwise the
> > > WARN_ON could not distinguish between a migration waiter and a surprise
> > > gup.
> > 
> > Sorry for the delay; been a bit busy.  I tested both of these patches on
> > top of this one (separately, of course):
> > 
> > http://www.spinics.net/lists/linux-mm/msg63919.html
> > 
> > I think that's the one you were referring to, if not send me a pointer
> > to the correct one and I'll give it another shot.  Both patches still
> > segfaulted, so it doesn't appear that either of these solved the
> > problem. 
> 
> I see. Does THP have to be enabled or does it segfault even with THP
> disabled?
> 

On a semi-related note, is the large machine doing anything with xpmem
or anything that depends on MMU notifiers to work properly? I noted
while looking at this that THP migration is not invalidating pages which
might be confusing a driver depending on it.

-- 
Mel Gorman
SUSE Labs
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